MGS uses it to decide between firing a gun and lowering it (slowly release square and you will lower, quickly release and you will fire). Also it uses shoulder button pressure to decide how far to shift left/right when in first person mode. I think there's other stuff too.
When holding hostages in MGS3. if you push the button firmly you slit their throats. My Snake has severe case of butterfingers with hostages, unfortunately for them.
The next time you want to make a joke, just assume it won't be funny and don't bother.
I make as many unfunny jokes as I frickin want, thank you very much.
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